Optical fibers are optical waveguides and are used to guide light. Optical fibers can be single-mode fibers that support only one traverse waveguide mode or multi-mode fibers that support two or more traverse modes. A multimode fiber (MMF) can be used to direct light in multiple modes for various applications such as applications requiring guiding light at high optical power levels.
Some applications require a spatially uniform distribution of light over the cross section of a multimode fiber. Examples of such applications include, illumination devices in lighting applications, optical local-area-networks (LANs) over MMF and image encryptions, fiber-based genetic analysis and functional genomics such as Massively Parallel Signature Sequencing (MPSS) and molecular interactions.
Mode scrambling has been a well-known technique to improve the uniformity in multi-mode fibers, different approaches have been demonstrated: (i) the modification of multi-mode fiber itself, such as through extremely high temperature annealing, or special fabrication procedure in the cladding; (ii) twisting plastic optical fiber instead of traditional MMF; (iii) selecting one special mode through mode coupling. These approaches can suffer from one or more disadvantages such as uncertainty or extreme requirements during manufacturing, increased cost of fiber, considerable optical loss caused by various factors in these techniques.